IMHO don't bother trying to use Itunes to TRANSFER stuff to a sd card, it really doesn't work well for what you want to do.
What to to do, well here is what I did and it works very very well.
1) rip the CD's into Itunes, this works good
2) open microsoft media player
3) it will automatically go in and load all your itunes stuff, along with any other albums you have
4) in media player drag whatever you want to listen to to the "save list"
5) select synce and select what drive you want it burned to
6) insert into your truck
I did this on our silverado. about 50GB of music, something over 10000 albums (CD's to you young guys!)
if you want playlists, create playlists in media player, and drag the playlists to the save list and it will sync it as playlists
I've done this with SD cards, or usb drive. both behave the same in my truck
